This invention relates generally to a method for the production of continuous sheathed cable. Specifically, the invention is directed to a method for producing continuous sheathed cable that will not transmit gas or vapors and, accordingly, is usable in corrosive or explosive ambient environments.
The improved method permits the continuous production of sheathed corrugated cable utilizing a foam of the closed cell type to prevent passage of gases or vapors. The composite cable formed by the instant methodology includes an insulated and often jacketed conductor or conductor ensemble, an outer metal corrugated sheath having a continuous welded seam, and a layer of closed cell foam disposed between the conductor assembly and the outer sheath. The improved method includes extruding a layer of foam around the insulated conductor, forming an outer sheath to encase the foam, and activating the foam by application of heat (for an initially non-foamed type) to expand the foam and fill the space between the inner and outer members. The barrier foam may be continuously or periodically extruded along the length of cable; and may be foamed in situ or prior to its application to the cable.
Many national and local building and electrical codes require sealed, sheathed cable to meet rigorous standards with regard to the transmission of gases or vapors through the core of the cable. One such standard is set out in the National Electrical Code promulgated by the National Fire Protection Association at Article 501, Paragraph (e)(2) which limits gas or vapor flow through a cable to a maximum of 0.007 cubic feet per hour of air at a pressure of 6 inches of water. The sheathed cable produced by the improved method of the present invention fully meets the National Electrical Code standard.
Accordingly, it is an object of this invention to provide an improved method for production of continuous sheathed cable.
It is another object of this invention to provide an improved method for producing sheathed cable which is impervious to the passage of gas or vapors.
It is another object of this invention to provide an improved method for producing sheathed cable utilizing an activatible closed cell foam.